The semiconductor fabrication industry continues to source volatile metal containing precursors for vapor deposition processes, including chemical vapor deposition (CVD) and atomic layer deposition (ALD), for fabricating conformal metal containing films on substrates, such as: silicon, metal nitride, metal oxide and other metal-containing layers, using these metal-containing precursors.
Barium and strontium containing precursors are especially sought after for the deposition of thin barium and strontium oxide containing thin films, such as: barium strontium titanate oxide (BST) for advanced memory device manufacture. Although there are fluorinated barium precursors which have excellent volatility (ref), their use for BST manufacturing is effectively precluded, since fluoride ion can form in the oxide film and act as a charge carrier, which degrades the dielectric constant of the oxide film.
Thus, there is a strong need for unfluorinated barium and strontium precursor compounds, but such compounds are scarce, especially so for barium. This stems from the large ionic radius of the barium+2 ion requiring ionic ligands which can provide a coordinating environment sufficient to provide compounds, which are monomeric or dimeric in barium. If this requirement is not met, the barium compounds tends to form highly associated or polymeric structures of limited volatility. However, even if monomeric or dimeric structures can be achieved, they may still not possess the thermal stability required to survive the high sublimation or distillation temperatures required for their vaporization. For all of these reasons, unfluorinated barium precursors, which are monomeric or dimeric, thermally stable, readily volatile and highly suited to BST manufacture by ALD or CVD, are extremely scarce, but highly sought after.
The prior art has attempted to provide precursors for these applications. However, none of the metal complexes in the prior art share the special characteristic of the complexes disclosed in the present invention. The compounds disclosed herein are exceptional in their volatility and thermal stability under conditions of vaporization. This makes them highly effective as precursors for BST film growth and any other application which requires volatile sources of barium. Similarly, these same ligand systems can also be applied to make volatile strontium, magnesium, radium or calcium precursors.
Related prior art to the present invention includes:
Harder, S. (2002); “Homoleptic beta Diketiminate Complexes of the Alkaline Earth Metals: Trends in the Series Mg, Ca, Sr, and Ba”; Organometallics 21(18), 3782-3787.
U.S. Pat. No. 5,319,118
El-Kaderi, H. M. and M. J. W. Heeg, C. H.; (2004). “Sandwich Complexes of the Heavier Alkaline Earth Metals Containing 5-Diketiminato Ligand Sets.” Organometallics 23: 4995-5002.
M. J. Saly, M. J. Heeg and C. Winters, Inorganic Chemistry, publication date (Web) Apr. 27, 2009.
B. Sedai, M. J. Heeg and C. Winter, Organometallics, 2009, 18 (4) p 1032-1038.
Timo Hatanpaa, Marko Vehkamaki, Ilpo Mutikainen, Jarno Kansikas and Mikko Ritala “Synthesis and characterization of cyclopentadienyl complexes of barium: precursors for atomic layer deposition of BaTiO3” Dalton Trans., 2004, 11811188.
H. Schmann, J. Gottfriedsen and J. Demtschuk “Synthesis and structure of eta-5 pyrrolyl complexes of calcium and strontium” Chem. Commun., 2091-2092, 1999).
WO 2009/086263A1.